1. Field of the Invention
The present invention relates to a turntable for a disk storage medium and a disk drive including the turntable.
2. Description of the Related Art
Apparatuses for reading or writing digital information optically and/or magnetically from/on a removable disk storage medium have been getting more and more popularized.
FIG. 14 schematically illustrates a configuration for a disk drive 100 as an example of such apparatuses. The disk drive 100 shown in FIG. 14 is for use to optically read and write information from/on a disk 101. As shown in FIG. 14, the disk drive 100 includes turntable 102, motor 104 as a drive source for spinning the turntable 102, read/write head 105 for reading or writing information from/on the disk 101, and clamper 103 for securing and supporting the disk 101 onto the turntable 102.
The turntable 102 includes a center boss 102A, which is to be inserted into the center hole 101A of the disk 101 when the disk 101 is mounted thereon and to which a yoke 107 made of a magnetic material has been attached. In this disk drive 100, the turntable 102 is directly fitted with the rotating shaft (not shown) of the motor 104.
The read/write head 105 moves in the direction indicated by the arrow 153 in FIG. 14 (i.e., in the disk radial direction) using a main shaft 106L and a jackshaft 106R as respective guides. A magnet 103A has been fitted within the damper 103.
To load the disk 101 into this disk drive 100, the disk 101 is moved downward as indicated by the arrow 151 in FIG. 14 so as to be mounted onto the turntable 102 with its center hole 101A engaged with the center boss 102A of the turntable 102. Thereafter, the damper 103 is also moved downward as indicated by the arrow 152 in FIG. 14 so as to approach the disk 101. In this case, the magnet 103A is attracted toward the yoke 107. Thus, the damper 103 forces the disk 101 onto the turntable 102 and fixes it thereon. According to another known technique, a force may be applied to the damper 103 in the direction indicated by the arrow 152 by using an elastic member such as a spring instead of the yoke 107 and magnet 103A.
Once the disk 101 has been fixed on the turntable 102 in this manner, the motor 104 starts to rotate the turntable 102, thereby spinning the disk 101. Then, the read/write head 105, which has been moving in the direction indicated by the arrow 153, stops at a predetermined position to read or write information from/onto the disk 101 there.
Hereinafter, the structure of the conventional turntable 102 will be described in further detail.
FIGS. 15 and 16 are perspective views respectively illustrating the top and bottom of the turntable 102. FIGS. 17a-17c illustrate projections (FIGS. 17a and 17c) and a cross-sectional view FIG. 17b of the turntable 102. In FIGS. 17a-17c projections of the top and bottom of the turntable 102 are illustrated in FIGS. 17a and 17c, respectively, and a cross-sectional view of the turntable 102 taken along the line XVII—XVII is illustrated in FIG. 17b. As shown in FIGS. 15, 16 and 17a-17c the center boss 102A and a bottom boss 102B have been formed on the top and bottom of the turntable 102, respectively. Also, a center hole 102C has been formed so as to go through the center boss 102A and the bottom boss 102B. The rotating shaft of the motor 104 has been inserted into, and fitted within, this center hole 102C. In this case, the shaft is normally. interference-fitted within the center hole 102C. Alternatively, the shaft may also be transition-fitted within the center hole 102C via an adhesive, for example.
After the turntable 102 has been secured onto the rotating shaft of the motor 104 in this manner, the yoke 107 is moved downward as indicated by the arrow 154 in FIG. 18 so as to be embedded at a predetermined position of the turntable 102. Then, the turntable 102 is now ready to spin the disk 101 once the disk 101 is mounted thereon.
The turntable 102 is molded out of a resin. Generally speaking, when a resin or metal is molded with a die, the molded product should preferably have a uniform thickness. Also, even when the material is molded plastically without using a die, it is preferable to eliminate unnecessarily thick portions as much as possible. For that purpose, the center boss 102A of the turntable 102 is provided with a hollow portion 102D and a shaft center boss 102E is further formed inside the center boss 102A as shown in FIGS. 15 and 17a-17c. As a result, the shaft center boss 102E and the bottom boss 102B are joined together via a portion 201 and the center hole 102C extends through both the shaft center and bottom bosses 102E and 102B as shown in FIGS. 17a-17c. This portion 201 is continuously formed so as to surround the shaft center boss 102E and the bottom boss 102B entirely.
Normally, unless the temperature of a product that has been molded out of a resin or metal with a die changes uniformly everywhere, the material of the molded product will shrink non-uniformly as the material is cooled. As a result, the product will be partially deformed (i.e., so-called “sink marks” will be created). To avoid this unwanted situation, it is preferable to minimize the percentage of portions that are not exposed on the outer shell of a molded product.
In the conventional turntable 102, however, the portion 201 of the product made of resin is much thicker than any other portion that makes up the center hole 102C as shown in FIGS. 17a-17c. In other words, the portion 201 has some internal parts that are relatively distant from the outer shell as compared with portions 202 and 203 of the shaft center boss 102E and bottom boss 102B. Accordingly, when the resin material is molded into this turntable 102, the molded material will have a non-uniform temperature distribution. Thus, part of the material will shrink differently.
As a result, that portion 201 of the molded material is drawn in the directions indicated by the arrows 154 and 155 in FIG. 17b, thereby creating sink marks 204 and 205 there as shown in FIG. 19. In FIG. 19, the sink marks are identified by the two reference numerals 204 and 205. Actually, though, sink marks are created all around the center hole 102C. Thus, the sunken portions will have an increased inner diameter.
The storage capacity of a disk storage medium like this has recently been increased by leaps and bounds. To make full use of that high capacity, the disk needs to be rotated with higher and higher precision. That is to say, it has become more and more necessary to minimize waving or fluttering of a disk being rotated.
However, once the sink marks 204 and 205 have been created on the inner surface of the center hole 102C, the shaft of the motor 104 will be inserted into the center hole 102C so as to tilt along the inner surface of the center hole 102C that has been deformed by the sink marks 204 and 205 as indicated by the dashed lines 104A in FIG. 19. As a result, the turntable 102 will also tilt with respect to the motor 104. In such a state, when the motor 104 is rotated, the disk 101 being rotated will flutter. Then, information cannot be read or written from/on the disk 101 as intended.
FIG. 19 illustrates a state in which the shaft of the motor 104 inserted has just reached a midpoint of the center hole 102C. Even if the shaft inserted has gone through the center hole 102C, the shaft will also rest on the deformed inner surface of the center hole 102C with the sink marks 204 and 205. Accordingly, friction will be caused irregularly between the shaft inserted and the inner surface of the center hole 102C other than the sink marks 204 and 205. Thus, the inner surface of the center hole 102C might be further deformed. For these reasons, it is difficult to ensure sufficient fluttering precision for the turntable 102 that has been irregularly mounted on the shaft in this manner.